(i) Field of the Invention
The present invention relates to a displacement type fluid machine such as a pump, a compressor and an expander.
(ii) Description of the Related Art
As conventional displacement type fluid machines, there are known a reciprocating fluid machine wherein a working fluid is driven by the manner that a piston repeats a reciprocation in a cylindrical cylinder, a rotary (rolling piston type) fluid machine wherein a working fluid is driven by the manner that a cylindrical piston is eccentrically rotated in a cylindrical cylinder, and a scroll fluid machine wherein a working fluid is driven by the manner that a pair of fixed scroll and orbiting scroll which have spiral wraps and stand up on end plates are engaged with each other and the orbiting scroll is gyrated.
The reciprocating fluid machine has some advantages in easiness of manufacture and inexpensiveness because of its simple construction. On the other hand, because the stroke from suction completion to discharge completion is short as 180.degree. of the shaft angle so as to increase the flow velocity in discharge process, the reciprocating fluid machine has a problem that its performance deteriorates due to an increase of the pressure loss. Besides, because it is necessary to reciprocate the piston, the rotating shaft system can not be completely balanced. This causes another problem of a great vibration and noise.
In the rotary fluid machine, because the stroke from suction completion to discharge completion is 360.degree. in the rotational angle of a rotating shaft, such a problem as an increase of the pressure loss in discharge process is less severe than in the reciprocating fluid machine. But, because the working fluid is discharged once per shaft rotation, there is a relatively wide variation of the gas compression torque. This causes a similar problem of vibration and noise to that in the reciprocating fluid machine.
In the scroll fluid machine, because the stroke from suction completion to discharge completion is long as 360.degree. or more in the rotational angle of the rotating shaft (usually about 900.degree. in case of a scroll fluid machine practically used as an air conditioner), the pressure loss in discharge process is little. Besides, because there is formed a plurality of working chambers in general, the variation of the gas compression torque in one rotation is little. This causes less vibration and noise. The scroll fluid machine is therefore advantageous on the above points. In the scroll fluid machine, however, it is necessary to maintain the clearance between the spiral wraps in engagement and the clearance between the end plate and a wrap tip. For this purpose, working with a high accuracy is required. This causes a problem of expensiveness in working. Besides, because the stroke from suction completion to discharge completion is long as 360.degree. or more in the rotational angle of the rotating shaft, there is a problem that the longer the period of compression process is, the more the internal leakage increases.
One kind of displacement type fluid machine wherein a displacer for displacing a working fluid does not rotates relatively to a cylinder having sucked the working fluid but revolves, namely, gyrates with a substantially fixed radius to carry the working fluid, is proposed in Japanese Patent Unexamined Publication No. 55-23353 (cited reference 1), U.S. Pat. No. 2,112,890 (cited reference 2), Japanese Patent Unexamined Publication No. 5-202869 (cited reference 3), and Japanese Patent Unexamined Publication No. 6-280758 (cited reference 4). Such a displacement type fluid machine as proposed therein comprises a petal-shaped displacer having a plurality of members (vanes) radially extending from the center of the displacer, and a cylinder having a hollow portion of substantially the same shape as the displacer. The displacer gyrates in the cylinder to displace a working fluid.
The displacement type fluid machine disclosed in the above cited-references 1 to 4 has the following advantageous characteristics. Because it has no reciprocating part unlike the reciprocating fluid machine, its rotating shaft system can be completely balanced. This brings about a little vibration. Besides, because the sliding velocity between the displacer and cylinder is low, it is possible to relatively reduce the friction loss.
In this displacement type fluid machine, however, because the stroke from suction completion to discharge completion in each of working chambers defined by the vanes of the displacer and the cylinder, is short as about 180.degree. (210.degree.) of the rotational angle .theta.c of the rotating shaft (almost a half of that of a rotary fluid machine and in the same extent of that of a reciprocating fluid machine), there is a problem that the flow velocity in discharge process increases and so the pressure loss increases to deteriorate the performance of the machine.
A displacement type fluid machine for solving the above problems is proposed in Japanese Patent Unexamined Publication No. 9-268987 (cited reference 5).